Terrorists using deep-sea grappling hooks attached to fishing trawlers could intercept the UK’s network of undersea communications cables, a report has warned.

It said they remained "uniquely vulnerable" to sabotage despite 97% of global communications being transmitted through fibre-optic cables.

The report, written by Tory MP Rishi Sunak for right-leaning think-tank Policy Exchange, said a successful attack on Britain's network would be a "crippling blow" to the country's security and economy.

"Whether from terrorist activity or an increasingly bellicose Russian naval presence, the threat of these vulnerabilities being exploited is growing," the report said.

"A successful attack would deal a crippling blow to Britain's security and prosperity. The threat is nothing short of existential.

"The result would be to damage commerce and disrupt government-to-government communications, potentially leading to economic turmoil and civil disorder."